Recent manufacturing breakthroughs have made it possible to manufacture inexpensive, single use cameras. Such cameras typically include all the basis necessities for capturing an image on film, but at the same time are constructed from inexpensive materials and hence can either be discarded after a single use or recycled by a manufacturer and resold. The necessary features in such a single use camera include a roll of film, a taking lens, a shutter release, a film advance and a viewfinder.
For single use cameras to be manufactured profitably, it is essential that they be capable of being manufactured from inexpensive materials and with a minimum of assembly steps. To accomplish this, it has been the practice of many single use camera manufacturers to use an "air viewfinder" to act as a pointing and framing guide for the camera user. An air viewfinder typically is simply an opening extending through the camera from front to back, the central axis of the opening extending generally in the same direction as the focal axis of the taking lens of the camera. Alternatively, an air viewfinder may include a framing guide, such as a sight, which can be a plastic member disposed within the viewfinder to assist the user in determining the boundaries of an image to be photographed.
For instance, U.S. Pat. No. 4,812,866 to Ushiro, et al., describes a molded front cover of a single use camera which has integrally molded therein a single lens. The lens can be either a taking lens or a viewfinder lens. Such a viewfinder does not yield an optically enhanced image, however.
Conversely, viewfinders in conventional cameras are "optical viewfinders". An optical viewfinder provides an optically aided view of the image to be captured on film. An optically aided view can more accurately convey to the user the boundaries of the image to be captured. An optical viewfinder employs two or more viewfinder elements, or lenses, mounted in a holder. In multiple-use cameras, which are considerably more expensive to manufacture than single use cameras, multi-lens viewfinders are assembled from separately manufactured lenses. This multi-lens viewfinder design has been avoided in single use cameras, however, because of the prohibitive cost. To incorporate such viewfinders in single use cameras, it has been necessary to manufacture each lens separately, assemble the lenses to form a viewfinder system and then incorporate the viewfinder system into the camera. Not only do the separate steps of manufacture and assembly impose extra cost in their own right, extra care must be taken during assembly to ensure that the lenses are kept clean and aligned properly, further adding to the expense.
To reduce cost, it would be desirable to form the viewfinder system in one molding process. Until now, however, no method has existed for forming an optical viewfinder system in a single molding process. The inability to form such a system arises from the necessity that the lenses be curved to present an optically aided view of the image to be photographed. As is known in molding technology, curves and indentations in an object to be molded create "undercuts," or protrusions, into the molded object. These undercuts prevent the molded object from being ejected from a typical mold without destroying either the mold or the molded object.
While it is known to mold in a single molding process items having undercuts, the known techniques have yet to be applied to the lens-crafting art. The difficulty with manufacturing lenses lies in the strict requirements for mold surface position and texture. The surfaces of a lens-forming mold must be highly polished in order to yield a product with surfaces of optical quality without post-molding polishing of the formed lenses.
Thus, a need has arisen for a method of producing an optical viewfinder system in a single-step molding process, despite the presence of undercuts which make part ejection difficult.